Gradation of microcapsule wall porosity by deposition of polymer mixtures (Eudragit RL and Eudragit RS). Phase separation of polymer mixtures and effects of external media and conditions on release.

With the aim of increasing flexibility in controlling release from microcapsules, mixtures of wall polymers varying in porosity were investigated by phase separation. Eudragit RL and RS (polymethylmethacrylate linear backbone polymers) mixtures differing in polar substituent content and porosity were used as the wall material and were deposited using a non-solvent addition method. Release rates increased with polar group content of the mixtures, using theophylline, potassium dichromate or sodium chloride as model core materials.

Phase separation modulation and aggregation prevention: mechanism of the non-solvent addition method in the presence and absence of polyisobutylene as an additive.

The mechanism by which microcapsule aggregation is diminished in the presence of low concentrations of adjunct non-walling polymers such as polyisobutylene (PIB) in organic solvents is uncertain. It is here investigated by phase separation studies employing the non-solvent addition method (cyclohexane) in parallel with microencapsulation experiments, using Eudragit wall polymers and tetrahydrofurane (THF) as solvent with and without PIB. Polymer incompatibility leads to formation of two dilute liquid phases and emulsification from the outset.

The influence of a non-ionic surfactant on rectal absorption of virus particles.

A bacterial virus, suspended in three different vehicles, was introduced into the rectum of rabbits. The virus was detected in the circulating blood as early as 10 min after the administration. The quantity of virus found in blood and the duration of its presence, were enhanced when a non-ionic surfactant was used as vehicle of the virus.

Relation between individual and ensemble release kinetics of indomethacin from microspheres.

Indomethacin microspheres based on a combination of ethylcellulose and polyethyleneglycol were prepared using the solvent evaporation process. Release profiles of ensemble and individual microspheres were measured. Both were found to follow first-order kinetics, in contrast to what was expected.

Variation of population release kinetics in polydisperse multiparticulate systems (microcapsules, microspheres, droplets, cells) with heterogeneity of one, two or three parameters in the population of individuals.

Release kinetics of active substances from ensembles of microparticles such as microcapsules, cells, droplets and liposomes constituted of individual entities releasing their contents at constant rates may follow zero order, first order, sigmoid or biphasic equations. The release equation observed depends upon the statistical distribution of release-determining parameters among the population. Typical cases are presented in terms of the distribution of two parameters, payload (m infinity) and time for complete payload release (t infinity) which also define the release rate constant (k).